1. Field of the Invention
The invention relates to emulsions having outstanding stability and reproducibility batch to batch, made using specific emulsifiers and oils selected from silicone oil and mineral oil or combinations thereof. The emulsions of the present invention are of the W/O (water/oil) type.
2. Description of the Prior Art
For the preparation of emulsions of the W/O type, emulsifiers are used which preferably are soluble or dispersible in oil and whose HLB value generally is less than 5. Such emulsifiers are normally used in an amount of 10 to 20 weight percent, based on the weight of the oily phase. Examples of such W/O emulsifiers include the fatty acid esters of glycerin, polyglycerin, sorbitol or wool wax alcohols. As the fatty acid component, oleic acid or isostearic acid is generally used.
According to the state of the art, special difficulties arise in the preparation of water/oil emulsions whose oily phase consists partly or completely of silicone oil. Conventional emulsifiers based on polyol esters of fatty acids do not produce satisfactory emulsions with silicone oils. Special formulations have to be worked out in each case for particular problems.
For example, U.S. Pat. No. 4,268,499, page 1, line 6, discloses antiperspirant preparations in the form of W/O emulsions which consist of:
(a) 30-60 parts by weight of an aqueous solution of an astringent, e.g., aluminum chloride, as a discontinuous phase;
(b) 27-67.5 parts by weight of a volatile liquid with a boiling point below 250.degree. C., e.g., a cyclic dimethylsiloxane;
(c) 0.5-3 parts by weight of a W/O emulsifier with an HLB value of 2 to 10;
(d) 1-5 parts by weight polyoxyalkylene-polysiloxane copolymer; and
(e) 1-5 parts by weight of an O/W emulsifier with an HLB value of 11 to 17;
wherein components (a) to (e) add up to 100 parts by weight.
Furthermore, for the preparation of W/O emulsions whose oily phase consist of silicone oil or contain this oil in a predominant amount, emulsifiers are commercially obtainable which consist of a solution of polyoxyalkylene-polysiloxane copolymers in a cyclic siloxane. These products are, however, not satisfactory in all respects. The W/O preparations must be storage stable in order to ensure an adequate shelf life and a constant product quality. The emulsions must maintain a constant consistency over a period of several months, and neither oil nor water may separate out. This storage stability must, moreover be maintained at temperatures ranging from −5° C. to +40° C. There are, however, still particular difficulties with preparing stable W/O emulsions having silicone oils as the oily, continuous phase, wherein the silicone content is higher than 20 weight percent and preferably, higher than 30 weight percent, based on the total weight of the emulsion, and/or which contain, in addition to the silicone oil, other oily substances, such as, paraffin oils, ester oils or liquid or solid waxes, such as, vegetable, animal or mineral waxes. The W/O emulsions prepared from such mixtures of silicone oil and carbon-based organic oils using emulsifiers of the state of the art, generally show inadequate emulsion stability and break within hours or days. Even the preparation of a briefly stable emulsion is frequently impossible.
Copolymers are known in which polyoxyalkylene groups, as well as long-chain hydrocarbon groups are linked to a linear polysiloxane. The synthesis of such compounds is described in U.S. Pat. Nos. 3,234,252, 4,047,958, 3,427,271 and 2,846,458. The synthesis is preferably accomplished by adding an olefin with, for example, 6 to 18 carbon atoms, and a polyoxyalkylene ether of an olefinically unsaturated alcohol, e.g., the polyoxyalkylene ether of allyl alcohol, to a polydiorganosiloxane having SiH groups, the addition being carried out in the presence of a catalyst containing platinum.
According to U.S. Pat. No. 4,381,241, these copolymers can be used as emulsifiers for the preparation of W/O emulsion of salt solutions in liquid hydrocarbons, which can be used as drilling liquids. There is no indication, however, that such compounds could be suitable for the preparation of W/O emulsions, the oily phase of which consists of silicone oil and, optionally, of other carbon-based organic oils or waxes.
U.S. Pat. No. 4,698,178, issued Oct. 7, 1987, incorporated herein by reference, is perhaps the most significant in the art of preparing water in oil emulsions. This patent, now expired, teaches that specific silicone emulsifiers can be used to improve the stability of water in oil emulsions. Silicone emulsifiers of the type disclosed in the '178 patent are alkyl dimethicone copolyols. The patent claims specific ranges of polyoxyalkylene oxide moiety in the compound. The so called “p” value has a proviso that the molecular weight of that group range from 250 to 2,000 molecular weight. The emulsifiers suggested by this application, while an advance, result in products that can separate upon standing, resulting in batch to batch variation in the preparation of emulsions.